01 of the environment The dynamic nature - E … · components of the environment. ... the environment is subjected to many changes. ... Black ants, ants, centipedes, scorpions and

1For free distribution

• investigate the various interactions among the different

components of the environment.

• understand the importance of the inter-relationships among the

different organisms for their survival.

• understand how the various interactions take place among

components, help to maintain the dynamic nature of the

environment.

By the end of this Chapter, you will be competent to...

The dynamic natureof the environment01


There are living components as well as non-living componentsin our environment. Since there are various inter-relationships amongthese components, the environment is subjected to many changes.

Table 1.1 - Some food relationships among plants and animals.

Observe the Table 1.1. Here the interactions between the

organisms in the three columns are indicated by arrows. By studying

it, you may understand that the herbivore directly and the carnivore

indirectly depends on green plants. The reason

for this is, only green plants can produce their

own food.This process is known as

photosynthesis. But there are some autotrophic

green plants adapted to catch insects and absorb

the nutrients after digesting them. By this way they

get extra nutrition needed. These are known as

insectivorous plants. Pitcher plant Nepenthes,

sundew and utricularia are some examples.

Fig. 1.2 -Insectivorous

plant (Pitcher plant)

1.1 The interactions among organisms

1.1.1 Interactions based on foodInteractions among plants and Animals

Green plant Herbivore Carnivore

Mango plant Squirrel Cat

Grass Rabbit Fox

Sunflower plant Snail Caucal

This is the dynamic nature of the environment. These

interactions can be well understood by observing the

nature closely.Some observations which show the interactionsamong organisms are ;

• A butterfly sucking nectar from a flower

• A cat killing and eating up a rat

• A creeper winding up the trunk of a tree to climb

upwards.

Fig.1.1- Butterfly sucking

nectar from a flower.

Interactions between organisms could be cartogorized as follows;


Let us try to identify some relationships between plants and

plants based on food.

You may have heard of Loranthus and Cuscuta. They are two

types of plants which grow on other plants. Both these plants send

their roots into the host plant and absorb the nutrition they need from

the host plant. Such a relationship, where only one

of the two organisms involved are getting the

benefit is called parasitism. The plant which is

benefitted is called the parasite.

Parasitic plants such as Loranthus posses green

leaves, hence can prepare its own food. Such

plants will only absorb water and minerals from the

host plant. These plants are called semi - parasites.

(Fig.1.3)

But Cuscuta which has no green leaves, absorbs

all the essential nutrients from the host plants.

Hence Cuscuta is a total parasite. (Fig.1.4) Total

parasitic plants are more harmful to the host than

semi-parasitic plants.

Carnivores depend directly on another animal for their food.

When they kill an animal and take it as food, food is known as the

prey, while the carnivore is known as the predator. As an example,

when a leopard hunts and eats a deer, the deer is the prey while the

leopard is the predator.

There are occasions a number of animals

depend on the same prey.(Fig.1.5). Here, there

is a competition among the predators and the

stronger one will succeed.

There are occasions that animals depend

on each other for the mutual benefit of both. It is

called symbiosis. Here both animals are benefitted.

Interactions among Plants and Plants.

Interactions among Animals and Animals

Fig.1.4 - Cuscuta

Fig. 1.3 -Loranthus

Fig. 1.5 -An animal

eating a prey


Such a relationship is also seen between ants and aphids. Aphids

feed on plant juices. A part of the plant juice which contains sugar is

sent out of the body of the aphid. The ants feed on this sugar solution.

In turn, the ant takes the aphids to new plants in order to find more

food. Hence both are benefited.

You may have often seen crows picking

up the ticks that live on the skin of cattle. The

cattle seem to be very tolerant of the crows in

such instances. That is because this is mutually

beneficial. The crow gets its food while the

cattle gets rid of ticks.

An interesting relationship exists between

sea anemone and a certain species of fish. The

sea anemone has poisonous tentacles. The fish

who lives among those tentacles gets protection

since the sea- anemone attacks any predator which

comes to catch the fish.

Another important inter-relationship based

on food is parasitism. Here the parasite is often

smaller than the host and always benefitted from

the host. As a result, the host is affected

The ticks that live on animals such as

cattle and dogs as well as the round worms

and thread worms that live inside the intestine

of man are examples of parasites.

Adult mammals feeding their

offspring is another wonderful food

relationship between animals and animals.

Mammals feeding their young with breast

milk is a good example for this. (Fig.1.8)Fig.1.8 - Feeding the young

Fig. 1.6-Aphid and ant

Fig. 1.7 - Sea anemone

and fish


Green plants store the energy of the sun in food. All other

organisms depend on this food for their nutritional needs. To fulfil

these needs, organisms build up relationships among them which can

be indicated as in Fig. 1.10.

Since many animals may

feed on the same food, and also

the same animal may feed on

many kinds of food, Food chains

get interconnected to form a

complicated web.

These are known as food

webs. Figure 1.11 indicates a

food web that can be seen in a

small thicket.

Food chains and food webs

Assignment 1.1

Draw and label two food webs you may come across in

your garden and in a fresh water pond.

This type of relationship based of food, when arranged in a sequence,

is called a food chain. In a food chain, each organism represents a

link. The first link is the primary producer. This is always a green

plant. The second link is a herbivore. The links beyond this are

carnivores, but at times may be omnivores. Two links in the chain

are connected by arrows. The arrow head points to the direction of

the higher trophic level.

Fig.1.11- Food web

plant

owlhawk

fox

mouse

grasshopper

rabbitdeer

grass

magpic

squirel

caterpillar

Fig.1.10

grass

producer herbivore

rabbit

carnivore

jackal


Food as well as protection is also an important factor for the

survival of an organism. Organisms in the higher trophic levels of the

food chain are a threat to those at the lower levels. Therefore protection

is a major factor which ensures the survival of organisms.

Parental care

Animals adopt various methods to protect their young from enemies.

A B C

Fig 1.12 - Parental care

• Kangaroo protects the young inside its brood pouch and

feeds it for about nine months. ( Fig 1.12 A)

• Thilapia protects its young by taking them into its mouth in

the sign of danger. (Fig.1.12B)

• The entire herd of elephants provide protection to the newly

born young irrespective of who the mother is.(Fig 1.12C)

• Bees and wasps secrete a poisonous chemical and destroy

enemies who try to harm their young.

1.1.2 Inter-relationships of organisms based on protection

Fig.1.13

Do you know?The honour for being the most committed

parent should go to the male penguin.

The eggs laid by the female penguin is kept on

the feet of the male, covered over by its feathers

and protected without moving, at low

temperatures of around -40 0C even for one month,

untill the she-bird comes back.


Fig.1.14 - Camouflage among different animals

Observe Fig.1.14 carefully. It may be difficult to

identify each of those animals from its surroundings.

They possess colour patterns, body shape and other

body features blend with their living environment very

well. It helps to protect the animal from predators. Such

adaptations to suit the environment are called

camouflage.

Protective behaviours and strategies

Organisms have many behaviours which ensure their protection. Some

such behaviours are shown in Fig. 1.15.

Camouflage

Fig. 1.15 - Protective behaviours of certain animals

Lizards, when grabbed by an enemy, will shed its tail and escape.

Very soon a new tail is grown. This is called regeneration. Skink also

possess this ability. Deers and buffaloes live in groups for protection.

Black ants, ants, centipedes, scorpions and snakes paralyse their

enemies by introducing poisonous things into their bodies. The bristles

of a caterpillar and claws of a cat are also organs helping in protection.

Leaf insect Lizard Frog Fish

Curling patterns of

pangolinsnail in its shell Curling of

millipede

A species ofsnake

Assignment 1.2

Observe the strategies adopted by animals for protection

and prepare a book-let.

For free distribution8

The place where an organism lives is its habitat. Organisms

have various interactions with the habitat for food, water, light, and

protection.

Interactions of plants with the habitat

According to the specific environmental features of a habitat,

organisms too display particular features to obtain water, air and light

from that habitat. These specific features are called adaptations. Table

below shows certain habitats and the specific features of that habitat.

Cactus Sonneratia - ‘kirala’ Ipomea

Valisnaria Drynaria Mango

Fig. 1.16 - Plants adapted to suit the habitat

1.2.1 Interactions based on habitats

1.2 Interactions between organisms and the abioticenvironment

Table.1.2 - Environmental features of some plant habitats.

Habitat Specific features of the habitat

Xerophytic conditions Strong sunlight, high temperature, little

water in the soil

Mangroves Soil covered with salt water. Soil lacks air.

Strong sunlight.

Sandy beach Loose sandy soil. Strong wind. Sand is

intermittently covered with salt mixed water.

Strong sunlight.

Fresh water pond Covered with water. Little light reaching the

lower layers of pond.

Epiphytes Fixed on to trunks of other plants. No

direct contact with soil, low sunlight.

Small thicket Sufficient water, soil, air and light.


Let us identify how each one of the plants in Fig.1.16 are adapted

to get water, air and light in the relevant habitats.

Cactus – Grow under xerophytic conditions. Fixed to the soil by

roots. Leaves have turned into thorns, to minimize the transpiration.

And as the stem is fleshy and green, it is also adapted to store water.

Sonneratia – A mangrove plant. Plant is fixed to the soil, but some

roots grow upwards. These are known as respiratory roots

(pneumatophores). Since the soil lacks air, respiration is done by

these roots.

Ipomea – This is a plant that trails along the seashore. The roots

spread quickly over the soil in order to absorb rain water. Leaf surface

is shiny to reflect the sunlight.

Valisnaria – Aquatic submerged plant. Fixed to the soil by roots.

Leaves are dark green. Leaves are narrow and ribbon shaped to resist

the flow of water.

Drynaria – Epiphytic plant, attached to the surface of the host plant

by roots. Leaves fold up like a cup to hold back organic matter carried

by the wind. Stem is hairy for the same purpose. Divided large leaves

absorb sunlight.

Mango – Mango a typical terrestrial plant. It has a well developed

root system. Highly branched. Strong trunk.

Interactions of animals with the habitatThe specific features of some habitats of animals are indicated below.

Habitat Specific features of the habitat

Land The substratum is soil. Sorrounded by air.

Trees Branches of trees. Sorrounded by air.

Water Sorrounded by water.

Soil Sorrounded by soil.

Table 1.3 Some animal habitats

Assignment 1.3

Give one example which grow in each of the above habitats.

Write the special features of those, which they process to suit that

particular habitat.


Fig. 1.17 - Animals adapted for different habitats

The Fig. 1.17 shows some animals which live in several habitats.

The method of movement of animals not only help them to obtain

water and food, but also for their protection. Legs in terrestrial

environment, wings and feathers in aerial environment, elongated body

and fins in aquatic environment, elongated body to move through the

soil are several adaptations of animals in locomotion.

Every organism needs air and water to maintain the life. In

addition, plants need soil and light, while animals need food. In order

to get each of these factors organisms interact with their surroundings.

Let us find out what these interactions are.

Soil

You may notice that most plants in our surroundings are attached

to the soil. The soil helps them to stay erect. The plant is fixed to the

soil by roots. The root system divides into branches and penetrates in

the soil while absorbing water and minerals needed to the plant.

Soil is affected by the plants. Because of the roots penetrating

the soil, the soil gets loosen and makes it porous. This increases the

amount of air and water that is retained in the soil. Roots prevent the

erosion of soil. Also the dead animals and plants undergo decay and

add fertility to the soil. Plants grow well in a fertile soil. As a habitat,

soil is important to animals as well. Their dead bodies and waste

materials help to make the soil fertile. The earth worm that lives inside

the soil makes the soil porous and fertile, by decaying the organic

matter.

Assignment 1.4

Write down how each of the animals shown in Fig. 1.17 shows

methods of movement suited to the environmental conditions of that

particular habitat.

1.2.2 Interactions based on matter and energy needs


Water :- The most abundant chemical in the bodies of organisms is

water. Many biological activities of organisms, take place in a medium

of water. Further, water helps certain organisms to maintain the body

shape and rigidity. Stems of most herbs stay erect due to water.

When water is not available, they wilt. Plants have various adaptations

to preserve water.

Green plants use water as one of the raw materials in preparing

food. A part of the water absorbed by the roots is used in the

preparation of food while another part evaporates from the leaf surface

as water vapour. This loss of water

vapour from the leaf surface is called

transpiration. Transpiration causes

the water in the soil to be released to

the atmosphere. This is particularly

important in the water cycle.

(Fig 1.17). Transpiration causes a

continuous stream of water to be

drawn into the plants from the roots.

Along with this water, minerals too

enter the plant and moves to all parts

of the plant. Water is also useful to

maintain the body temperature in animals.

Air :- Air is a mixture of gases. The oxygen in it, is used for respiration.

Land animals get their oxygen from air while most animals that live in

water get the oxygen from water. They show various adaptations for

this. Land animals, including man has lungs for this purpose. Fish

living in water have gills.

Green plants use the carbondioxide of the air to prepare food. Carbon-

dioxide gets back into the environment

during respiration of organisms. Since this

carbondioxide is absorbed by plants for

food production, the composition of the

atmospheric air remains fairly constant. Plant

leaves have very tiny holes in their surface

called stomata. (Fig 1.19).

Fig. 1.18 - Water cycle

SunClouds

Raining

Reservoir

Plants

Fig. 1.19 - Arrangement ofstomata on the lower surface

of a leaf.


Air enters the plant through these

stomata. Oxygen needed for respiration

and carbondioxide needed for

photosynthesis is obtained from this air.

The oxygen needed for the roots is taken

from the soil air. Moving air is called wind.

The wind effects on plants indirectly.

Sunlight and heat energy

Green plants need sunlight to prepare food.

For this reason plants grow in search of sunlight.

They also get heat energy from the sun. As the

temperature of the environment goes up, the air

around the plant loses water vapour which in turn

increases transpiration. Therefore, plants living in

areas with a scarcity of water have adaptations to

reduce transpiration.

Some such adaptations are having;

• a shiny leaf surface, a layer of wax on the leaf surface,

• stomata sunk in pits

• leaves turns into thorns

Plants grow in dry climatic conditions (xerophytic) have very significant

adaptations to reduce transpiration. Cacti plant is an example for this.

Animals can see the surroundings because of light. Therefore

in addition to food and water, animals need sunlight too, to ensure

their existence. Eyes of bats are not sensitive to light, hence they fly

about in the night to seek food.

Temperature is a result of heat. All activities in plants take place

within a certain temperature range. Certain animals maintain their body

temperature constant whatever the surrounding temperature is. They are

called warm blooded animals. Various adaptations are seen in them to

maintain their body temperature at a constant level. Some examples are

having a covering of fur and production of sweat. Mammals and birds

are warm blooded animals. Reptiles and amphibians are cold blooded

animals. Their body temperature changes with the environment. Hence

during strong sunlight , they often hide at dark places.

Fig 1.21 Colouration of

leaves to absorb sunlight

Fig. 1.20 - Effect of wind on plants


Three factors which are highly changeable in the environment

are water, light intensity and temperature. The adaptations that organisms

show towards the changes of these factors are very interesting.

Perennation

Perennation is one of the adaptations shown by organisms to

ensure their survival during unfavourable environmental conditions.

Some of the reasons for perennation are lack of water, increase of

temperature and extreme cold.You may have seen how the grass on a playground dies off

during dry season, but with the rains, they sprout up again and become

green. The reason for this, is the underground stems (Fig 1.22). During

dry season, these underground stems remain below the soil. With the

rains, they produce new plants from the buds. The lotus plant too,

remains under the mud during the dry season and will sprout up again

from the buds.

Fig. 1.22 - Ginger plant and grass Fig. 1.23 - Tree during leaf fall

In the winter, most plants respond to the extreme cold by

slowing down or completely stopping their rate of growth. For this,

certain plants shed their leaves. Some plants shed their leaves during

very hot weather (Fig 1.23). Example: Rubber

Seeds often have a dormant period before germinating. This

dormant period is useful to overcome unfavourable conditions. The

hard covering of the seeds too is a useful strategy for overcoming

difficult conditions. All these are considerd as methods of perennation.

Among animals too, there are strategies to overcome difficult

environmental conditions. Examples are certain kinds of fish

(Kaawaiya, Magura) and the frogs that hide under the mud when the

pond dries up.

1.2.3 Interactions based on changes in environmental factors

Underground

stem


They hibernate under the mud till favourable conditions

return.In temperate countries, animals such as rabbits and squirrels

stay inactive inside holes in the ground or in hollows in trees. This is

called hibernation.

Migration

Animals migrate from one area to another for certain reasons

such as food shortage, unfavourable environmental conditions or for

reproductive purposes. In migration animals often take the same path

to return.

Migration is common among birds. With the approach of the cold

season in countries in the Northpole, certain kinds of birds fly over

thousands of miles of oceans to get the warmth in tropical countries.

Whales too migrate from the north seas to the tropical seas.

When the cold season is over, they migrate back to the North. Salmon

fish migrates only once during its life-time. They are born in the river,

later migrate to the Atlantic ocean where they grow to maturity. They

come back to the river to breed, and eventually die, never returning to

the ocean.

Migration does not

occur cyclically all the time.

Elephants and cattle migrate in

herds when there is a shortage

of food or water in their

environment and they go to

other places for food or water.

Fig.1.24 - Some migrant birds

Fig. 1.27 Path of migratory birds to Sri Lanka

paradise

fly catcher swallow

Sri Lanka

quail Indian Pitta


Recall an old house which has

been abandoned for a long time. There

may be some small weeds growing on

its walls, or there may even be small

herbs growing while their roots

penetrating into the wall and causing

cracks in the walls.

With further decay, the entire

house may come down and more

plants will grow. So that the place will

change beyond recognition.

It will now be clear to you, that even when environmental

conditions do not change, the living and the non-living environment

changes from a simple to a more complex state. This process is

called a succession.

A succession may start on the surface of an exposed rock or on

an open water body such as a pond. At the end, a permanent forest

may be formed. This is called a climax community. Since this process

undergoes a series of recognizable steps, it will take a long time to

happen.

1.3.1 Establishment of organisms in a barren environment

The surface of an exposed rock is unfertile. No plant can grow

on it. Yet you may have noticed whitish patches on certain places,

spread over it (Fig.1.27A). These patches represent lichens. Lichens

are autotrophic, and consist of fungal and algal varieties.

They can grow on very unfertile surfaces. As the lichens grow,

certain chemicals are secreted by them which cause the rock to a

process of chemical weathering. Further, dead parts of lichens gather

on the rock surface. Then action of decomposers will begin and the

process of soil formation is started.

Fig. 1.26 - An abandoned house

1. 3 Interactions between the living and the non-living

environment with time


The soil so formed eventually supplies a suitable substratum for

the seeds which get blown around. Plants such as moss, ferns, grasses

and small dicotyledons will get established on this soil (Fig.1.26 B).

These add more organic matter to the soil.

Gradually the soil improves in quality and quantity and, it paves

the way for more long-term plants (Fig.1.27C).

A B C D

Fig. 1.26 -Stages of a succession starting on an open rock

Succession is a fine example of a situation where organisms

build up the environment for themselves as well as provide opportunity

for other organisms too.With time, as plants grow herbivores and

next the carnivores and finally the decomposers will settle down,

eventually a climax community will be established. (Fig. 1.27D)

1.3.2 Establishment of organisms in a water body

Let us consider a pond as an example for an open water body.The

organic material in a pond is very little. We can see some plants floating

on the surface or emerged in the water. These are the pioneers in this

habitat. On death of these organisms, decomposers will act on them

and cause decay. The soil so formed will gather at the bottom and

finally raising the level of the pond and reducing the depth of the pond.

Fig. 1.27 - Stages of a succession


Around this time, certain kinds of reeds and bamboo will grow

close to the pond. With the death and decay of these plants, more soil

will be formed around the pond. The pond edge will get broader and

more plants will grow which eventually will grow into the pond.

As this process continues, more and more living and non-living

matter gets collected in the pond eventually filling up the pond with

soil. The soil is now suitable for the land plants to grow. Gradually the

pond will be converted to a forest.

1.3.3 Establishment of organisms in a cleared area

There are occasions where man

destroys forests for chena cultivation or

for other activities.Forests get destroyed

by bush fires or other natural reasons too.

In such cleared areas, small plants will grow

in a very short period of time. Because

there are some leftover seeds and roots in

the soil. If such an area is left undisturbed,

it will become a jungle again. In this way,

destroyed environments get rehabilitated, but it needs a long time to

happen.

The nature and type of the climax

community is determined by the environmental

conditions found there. The organisms which

are most suitably adapted to the

environmental conditions of that area, will

get established successfully in that particular

community.

Fig. 1.28 -Some stages of a succession in a pond

Fig.1.29-Reestablishment

of plants in a bare land

Fig 1.31- a scrubland


Organisms living on the earth live in different habitats.The soil

on the earth crust is directly important for the growth of organisms.

Let us consider, how the rocks are important for the growth of

organisms?

Weathering of rock occurs in two ways.

1. Physical weathering - Breaking up of rock into small pieces.

2. Chemical weathering – Separation of the chemicals making up

the rock.

1. Physical weathering

Physical weathering is the breaking up of the rock due to the

pressures and pulls acting on the rock. Temperature is one of the

factors causing weathering. Rock that is exposed to strong heat of

the sun during the day time, when subjected to sudden fall of rain or

the cooling during the night, it contracts and cracks up.

The breaking up of large pieces of rock into smaller pieces,

due to various factors is called physical weathering. Let us observe

how physical weathering can occur due to pressure.

1.4 Interactions take place in the non-living environment

Weathering of rock

Do you know?If cool water is poured into a heated glass, it will crackup

instantly due to the sudden contraction of the surface.

The volume of ice formed out of a certain volume of water is greater.

If a glass bottle filled with water, sealed and left to freeze will crack

up due to the pressure of the ice formed inside, as the volume of ice

will be greater than the volume of water.

Do you know?

4600 years back, the earth was a huge ball of air. It’s

temperature was around 40000C – 80000C. When this started cooling

gradually only the outer layer cooled to form a solid mineral crust.

These minerals gradually underwent weathering to form the soil.


From the above activity, you would have understood how

weathering takes place when rock gets carried down by fast flowing

water.

• Rocks on the ocean beaches are subjected to weathering by

being constantly hit by sand carried by the waves.

• Plants growing on the surface of large rocks send their roots

into the crevices of the rock. As the roots spread out and go

deep, resulting pressures will cause the cracks to widen and the

rock to break up into smaller pieces.

• Animals walking on the rock too cause the weathering of rocks.

2. Chemical weathering

In physical weathering, due to the breaking up of the rock into

small peices, the surface area of the rock increases. Now it can react

better with environmental factors such as water and air. Therefore

chemical reactions can take place faster. In this way, the speed of

chemical weathering gets accelerated after physical weathering.

Instances where chemical weathering occurs

• Carbondioxide of the air dissolves in rain water and then the rain

water becomes slightly acidic. The limestone, granite or iron ore

in rock will get dissolved off in such acidic water.

Activity 1.1

Put some pieces of stone into a bottle , add some water and

shake it vigourously.

After shaking for about 15 minutes, note how the sharp edges of the

pieces have got rounded.

Note the fine powder of rock gathered at the bottom of the bottle.

Assignment 1.4

Prepare a report on the following. Identify the factors that

cause weathering, and discuss how they bring about weathering.


• Lichens and moss growing on rocks retain moisture.This film of

moisture is acidic.Further the juices of fruits that fall on are also

slightly rocks acidic. This acidic solutions bring about chemical

weathering of the rock.

• Carbondioxide from the roots of plants dissolve in soil water and

form an acidic solution. This brings about chemical weathering.

• Dead bodies of organisms and the faeces are acted upon by

microorganisms. The solutions so formed are acidic and cause

weathering.

• Human activities too speed up chemical weathering. eg. Burning of

fuel by motor cars and factories emit sulphurdioxide and

nitrogendioxide dissolve. These gases dissolve in water and makes

it acidic. The acidic water falling on rock causes chemical weathering.

Living bodies are made up of organic matter.When they die,

activity of microorganisms convert the organic matter into simpler

compounds which are added to the environment.This process is called

organic decomposition.

Let us identify how the decomposition of dead organic matter occur.

Decomposition of organic matter

Activity 1.2 Identify the follwing instances in our environment and name

the organisms which cause decomposition in each case.

E – Carrot with mildew

A- Mushrooms growingon a cut down tree

B - A decaying logwith termites and

worms.

D – Leaf covered with fungal

growth

C – Fallen leavesdecaying under a tree


The pictures above show that decay of dead organic matter is

brought about by micro organisms such as bacteria, fungus as well as

macro organisms such as termites and worms.

These organisms are called decomposers.They decompose

not only dead organic matter but

also sewage.

Bodies of the organisms are

made up of materials which were

borrowed temporarily from the

environment. The function of

returning these materials to the

environment is done by the

decomposers.

Therefore decomposers

play a major role in recycling of

materials (Fig.1.32).

Fig.1.32

Minerals in the

soil

Plants

Animals

Death and

decay

You have seen that water flowing down on a rainy day is

sometimes brown in colour. Collect a sample of such water, keep it

aside for about a day and observe. You may see that the colour of the

water is clear and clay gets collected at the bottom of the vessel. The

reason for the brown colour of flowing water is due to clay particles

which get washed away with flowing water.

After the school vacation, you can see your classroom is

covered with dust. Dust is small particles of soil.These were brought

there by wind. The process of transporting soil from one place to

another and depositing it there is called soil erosion.

Erosion is caused by two major factors.

1. Water

2. Wind

Let us consider the factors affecting soil erosion caused by water.

Soil erosion

Cycling of organic matter


You would have noticed that the brown colour of the water

flowing down on the loose soil in the uncovered areas was more than

that of the land covered with grass or decaying leaves. This shows

that soil erosion is reduced by having a cover of living or non- living

organic matter over the soil.

Activity 1.3 Take a tin with holes at the bottom. Pour equal amounts of

water from an equal height at each instance and compare the colour

of the water flowing out.

(a) Uncovered hard soil

(b)Uncovered loose soil

(c) Uncovered soil at an incline

(d)Soil on a flat land covered with grass

(e) Loose soil covered with decaying leaves.

From the results of your activity, try to identify the instances when

erosion takes place most and when it takes place least.

Fig. 1.33 - Cover crops

The erosion takes place by wind is affected by the speed of the wind

and the nature of the soil. Now you know growing trees as wind

breaks and covering the soil with organic matter reduces soil erosion.


Now, it will be clear to you that the living and non-living

components of the environment interact with each other and thus

contribute to a great extent to maintain the dynamic equilibrium of the

environment. Further, the interactions among living and non-living things

will contribute to build a complex environment.

1. With the help of a food-web related to a pond, show the

interactions of plants and animals based on food.

2. Explain how a mango tree is adapted to obtain the basic needs

for its growth.

3. Explain how far hibernation and migration help in the survival

of organisms.

4. Explain how decomposition of organic matter helps in

maintaining the environmental balance.

5. Indicate the various stages of a succession, with a diagram and

explain it briefly.

Exercises

Documents

01 of the environment The dynamic nature - E … · components of the environment. ... the environment is subjected to many changes. ... Black ants, ants, centipedes, scorpions and